The evolution of communications networks (e.g. the Internet) has been accompanied by increasing demand by users for delivery of multicast services over such networks. Multicast services distribute, for example, news, entertainment or educational content, which is transported over the network from a single source node to a plurality of sink nodes. The source node is typically a multicast server, such as an Internet Protocol (IP) server connected to an IP data network that outputs the multicast content. The sink node is typically an end-user's communication device such as a personal computer (PC) connected to the network via a modem.
For high bandwidth applications, the use of Digital Subscriber Loop (DSL) technology, cable modems, satellite systems, and the like, are becoming increasingly popular as a means of coupling customer-premise equipment (CPE), such as personal computers (PCs) or Local Area Network (LAN) servers to the communications network. Many of these access technologies are based primarily on the use of an ATM switching network for data transport, which facilitates high bandwidth data transfer, while simplifying network provisioning and management. Multicast data from the source node is typically routed to the ATM switching network through an Internet Protocol (IP) service gateway (IPS GWY)). Each sink node (i.e. CPE) is normally connected to the ATM switching network via an access module (e.g. a Digital Subscriber Line Access Multiplexer (DSLAM); a cable headend; a wireless headend; a satellite base station; an optical line termination; or customer premise equipment).
When an end-user wishes to join a multicast session, a join request message originating at the end-user's CPE is forwarded to the IPS GWY. Upon receipt of the join request message, the IPS GWY joins the sink node directly to the multicast tree if the IPS GWY is already grafted to the multicast tree. If not, the IPS GWY establishes a connection with the multicast source node to establish a branch on the multicast tree. The IPS GWY joins the sink node to the multicast tree by performing standard IP routing to route the multicast traffic into a virtual channel used to provide DSL service to the end-user's CPE. Once the multicast source has been joined, high bandwidth multicast content originating at the source node is routed through the access module to the end-user's CPE over the end-user's channel, a switched virtual circuit (SVC) or a permanent virtual circuit (PVC), for example. This approach avoids supporting any IP protocols in nodes in the ATM switching network. However, a limitation of this approach is that it results in redundant duplication of multicast traffic within the ATM switching network.
In particular, two or more participating CPEs served by the same access module results in multiple copies of the multicast traffic being routed through the ATM switching network between the IPS GWY and the access module. This can degrade performance on access feeder trunks between the access module and the ATM switching network, due to bandwidth exhaustion. Furthermore, since the multicast packets traverse the ATM switching network via virtual channels (VCs) serving the respective CPEs, the quality of service (QoS) associated with the respective VCs is transferred to the multicast packets. This may affect the rate of transfer of the multicast packets across the ATM switching network and degrade multicast performance.
Accordingly, a way of grafting end-users to a multicast tree that minimizes duplication of traffic within the ATM switching network while preserving associated QoS is highly desirable.